Chevrolet GMC 6.6L Duramax Diesel 2020 Supplement Manual page 72

Adding Coolant
Caution
If coolant is changed or added,
always add enough to fill the
system completely or engine
damage may occur.
If more coolant is needed, add the
proper DEX-COOL coolant mixture
at the surge tank, but be careful not
to spill it.
Warning
Spilling coolant on hot engine
parts can burn you. Coolant
contains ethylene glycol and it will
burn if the engine parts are hot
enough.
Warning
Steam and scalding liquids from a
hot cooling system are under
pressure. Turning the pressure
cap, even a little, can cause them
to come out at high speed and
you could be burned. Never turn
the cap when the cooling system,
including the pressure cap, is hot.
Wait for the cooling system and
pressure cap to cool.
If no coolant is visible in the surge
tank, add coolant as follows:
1. Remove the coolant surge tank
pressure cap when the cooling
system, including the coolant
surge tank pressure cap and
upper radiator hose, is no
longer hot.
Vehicle Care
Turn the pressure cap slowly
counterclockwise about
one-half turn. If a hiss is heard,
wait for that to stop. A hiss
means there is still some
pressure left.
2. Keep turning the pressure cap
slowly, and remove it.
3. Slowly fill the coolant surge
tank (2). Do not let the coolant
level go above the indicated
mark in the tank until after the
engine comes to operating
temperature in Step 4.
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